c:\@Work\Perl\monks>perl -wMstrict -le
"my @seatlocs = (qw(A1.23BC U2.60L R2.32 C1.3L AB3.45E D45.1A), 'Some Bldg');
 ;;
 for my $loc (@seatlocs) {
   print qq{'$loc' },
         $loc =~ m{ \b [A-Z]{1} \d{1} \. \d+ [A-Z]* }xms
         ? 'Correct' : 'Invalid';
   }
"
'A1.23BC' Correct
'U2.60L' Correct
'R2.32' Correct
'C1.3L' Correct
'AB3.45E' Invalid
'D45.1A' Invalid
'Some Bldg' Invalid